It has been known for many years that a fluidic oscillator can be used to measure the flow rate of a flowing fluid.
Document FR 2 663 417 discloses apparatus for measuring the flow rate of a fluid by making use of a fluidic oscillator. The apparatus described therein comprises, from an upstream end to a downstream end: a metal screen for modifying the speed distribution of the fluid flow; and a slot that is elongate in an Oz direction and suitable for forming a fluid jet that oscillates in an Oxy plane perpendicular to said direction and within an oscillation chamber.
The oscillation chamber has a plurality of obstacles including one situated facing the slot and two lateral obstacles serving to define recirculation flows centered on said obstacles and enabling the fluid jet to be switched from one lateral obstacle to the other. The fluid jet thus adopts "oscillating" motion which takes place at a frequency that is representative of the flow rate of the fluid.
The oscillation frequency of the jet is detected, for example, by means of pressure pickups situated at the extreme points of the sweep of the jet of fluid, and connected to known electronic systems.
The oscillation frequency of the jet is associated with the flow rate of the fluid by prior calibration.
The measurement apparatus presents curves of error as a function of flow rate that are acceptable, given the intended applications.
Nevertheless, the Assignee has observed that in the presence of fluids, such as gases, conveying impurities (particles, dust, . . . ), the impurities can accumulate in the openings of the metal screen, thereby disturbing the distribution of speeds in the flow between said screen and the slot of the fluidic oscillator.
That phenomenon therefore runs the risk of degrading the performance of the measurement apparatus quite quickly, and after the apparatus has been in operation for a few years the openings can become completely obstructed, thus making any flow rate measurement impracticable.
The above contamination phenomena are made worse when the fluid concerned is hot water.